Electric clock



April 28, 1942. 1.. HAMMOND 2,231,493

ELECTRIC CLOCK Filed Feb. 13, 1951 6 Sheets-Sheet 2 I 3 [@IWQ 212 Q gumun 220 j? V6737??? g aaran fiimmmd W' ZK April 8, 9 L. HAMMOND 2,281,493

ELECTRIC CLOCK Y Filed Feb. 13, 1931 6 Sheets-Sheet 3 Aprii 28, 1942 L. HAMMOND ELECTRIC CLOCK Filed Fb, 13, 1951 6 Sheets-meet 5 "ZIP/6727;??? 2w ffiwm ma April 28, 1942. HAMMOND 2,281,493

ELECTRIC CLOCK Filed Feb. 13, 1931 6 Sheets-Sheet 6 Patented Apr. 28, 1942 ELECTRIC CLOCK Laurens Hammond, Evanston, Ill., assignor to Hammond Instrument Company, Chicago, Ill., a corporation of Delaware Application February 13, 1931, Serial No. 515,598

13 Claims.

My invention relates generally to time keepin devices, that is, devices having a timing function such as metronomes, recording meters of various kinds, and in fact, all devices in which constant speed of operation is an essential factor. The invention relates more particularl to improvements in synchronous electric clocks, that is,

clocks in which the speed of operation is con trolled by the timed impulses of an alternating or pulsating current.

Clocks of this type have come into general use because of their simplicity, quiet operation, durability and high degree of accuracy. The clocks of this type now on the market are for the most part driven by synchronous motors and have the pronounced disadvantage that they stop upon interruption of the supply of alternating current. Several means for overcoming this disadvantage have been proposed but have not come into use because of their commercial impracticability, even though the demand for a clock which will not stop upon interruption of the supply of cur rent is very great. The demand is especially present in many communities where the supply of alternating current is frequently interrupted due to electrical storms, shut-downs in the power generating stations and disconnections in the line necessary for repairs and alterations. Even in communities where the supply of current to the consumer is only very rarely interupted, the

supply of current to the individual clock is freserved as a stand-by movement to drive the hands of the clock upon interruption of the current, suitable clutch and stop devices being incorporated to cause operation of the clock by the stand-by movement upon interruption of the current supply to the synchronous motor. This attempted solution of the problem presents difllculties in manufacture, greatly increases the cost of the clocks, and is not entirely successful in operation because of the fact that a certain amount of time is lost each time the transfer is made from the'synchronous motor drive to the spring motor drive.

Another attempted solution involved the provision of a synchronous motor 'drive and spring motor drive connected through differential gearing with the hands of the clock, the spring motor drive being held against operation while the synchronous 'motor was in operation and vice versa. This attempted solution had the same disadvantages as enumerated above except that instead of losing time the clock would gain time. The reason for this gaining of time was that it always took a certain amount of time to stop one of the mechanisms and start the other, and hence there was a certain amount of overlap during which interval both mechanisms were operating, thus permitting the differentially movable member of the differential gearing to move twice its normal speed during this interval.

In the clock of the present invention there is, strictly speaking, no auxiliary clock movement. Generally, the clock comprises an induction motor geared to wind a spiral clock spring, the driving side of which is geared to a synchronous electric brake which acts in place of the escapement mechanism of an ordinary clock, and prevents the spring from unwinding at greater than a predetermined speed. The rotating part of the synchronous electric brake is also connected to a centrifugal mechanical speed governing mechanism. A pawl and ratchet mechanism prevents the spring from unwinding and rotating the induction motor backward when the current supply is interrupted. The synchronous electric brake is of course ineffective during an interval of cur-' rent interruption, but during such interval the mechanical centrifugal mechanism is effective to control the speed of operation of the clock. The moving parts of the centrifugal mechanism are continuously rotating so that the transfer of the speed control from the synchronous brake to the centrifugal mechanism is efiected without starting or stopping any part, and hence without loss of time.

It is thus the object of my invention to provide a clock in which the disadvantages of the prior clocks of this type are overcome and which has the advantages above described.

More specifically, the objects of my invention are to provide an improved synchronous electric clock which (1) Will operate during extended periods of current interruption;

(2) Will not require manual rewinding;

mechanism;

Join plates 22 and 24. Theclock of course mounted'in a suitable case, not shown, and has a face dial 30, an hour hand 40, minute hand 42. and second hand M,

Referring to the diagram of Fig. 11, the clock comprises an induction motor having an induction rotor 64, which, through the gear train 16,.

86, 90, 32, 98, I00, I04, I08, H0 and H2, rotates spring drum H4. The spring II8, the outer end (6) Has centrifugal means running freely when of which is secured to the drum II4, has its the current is being supplied at the correct frequency, which means, upon a current interruption, are immediately effective to control the speed of the clock mechanism;

inner end secured to the shaft H8, and through gear train I20, I22, I24, I28, I28, I30, I32, I34, I36 and I38, drives shaft I4. The toothed rotor i0 forms a synchronous brake in cooperation with the toothed poles forming part of a suitable magnetic field, and is rigidly secured to the shaft It. Also secured to the shaft I4 is a mechanical speed governing mechanism, shown in Fig. 11 as comprising weights 200 which are ing the electric motor mean ith one end of 205 connecmd to the shaft I4 through a resilient the spring and the other connecting the opposite end of the spring with the synchronous brake;

(10) Has the similar gears of each of the two trains supported by the same shafts and normally rotatable at the same speed;

(11) Has improved shaft bearings;

(12) Utilizes the centrifugal means as a means to prevent the rotor of the synchronous brake from hunting, and as a means for facilitating easily bringing the rotor of the synchronous brake into synchronism. I

Other objects will appear from the following description, reference being had td the accompanying drawings, in which:

Figure 1 is an elevation of the clock face;

Figure 2 is a plan view of the clock;

Figure 3 is a vertical sectional view thereof taken on the line 33 of Fig. 4;

Figure 4 is a right side elevation of the operatthe throw of the casing of the centrifugal mechanism;

Figure 9 is an enlarged vertical sectional view taken on the line 9-9 of Fig. 7;

Figure 10 is a developed sectional view showing particularly the gear trains;

Figure 11 is a diagrammatic view of the clock; Figure 12 is an elevational view of a modified form of mechanical speed governing means;

Figure 13 is a side elevation thereof; Figure 14 is an elevation of an escapement Figure 15 is a plan view of the escapement mechanism shown in Fig. 14; and

Figures 16, 17 and 18 show the different forms 5 clock may be more readily understood, the general features of construction and an outline of the operation will be presented first.

The clock' comprises three generally similar frame plates 20, 22 and 24. Studs 26, 23, conto raise the raceway 2I2 when the spring drum connection. t

. ii ibegins to rotate clockwise. The hands of the clock are driven by the train of gearing connected to the I I4 clockwise.

which connects the rotor I0 of the synchronous 39 brake and the shaft II0.

35 maintain it wound. When the spring is thus wound, a force will be transmitted to the shaft H0 and hence through the train of gearing to, the synchronous brake. Assuming that the synchronous brake has been set in motion at syn- 0' chronous speed (which is accomplished manually), the induction rotor will, through the two trains of gearing and through the spring I0, continue to rotate the synchronous brake and also the centrifugal mechanism which is resiliently shaft I4 and rotatable therewith. v

Upon an interruption of the supply of current, the spring 8 will of course tend to rotate the shaft Ht counterclockwise and the spring drum The clockwise movement of the spring drum II4 will, however, be arrested In a .short time by the pawl I13, so that all of the remaining energy stored up in the spring III will .be dissipated'through driving the train of gearing shown at the right in Fig. 11, and the shaft complishes this function. When the braking effect of the synchronous rotor is removed upon the interruption of the current, there is a tendency slightly to increase the speed of rotation of the shaft I4. Due to the inertia of the parts, this tendency is not manifestfor several seconds, and during this time the pawl I'll will, in the form of centrifugal governing mechanism shown in 'Fig. v11, have raised the'raceway 2I2 to the position shown in said figure, in which position the weights 200 of the centrifugal mechanism revolve in such close proximity to the lower portion of the raceway that any tendency of the nect plates 20 and 22, and studs 32, 34 and 30 shaft I4 to increase its Speed of rotation is pre- During this 00' period, however, the centrifugal mechanism vented by frictional contact of the weights with the lower portion of the raceway 2I2.

While this centrifugal governing mechanism does not form a perfect time regulating device, it has been found that within the degree of accuracy capable in commercial quantity production, it may be made sufficiently accurate that during a period of half an hour of operation the centrifugal mechanism will maintain the speed of the mechanism so nearly constant that the cumulative error during the half hour's perior of operation will not exceed more than a few seconds. Since current interruptions are usually of only a few seconds, or at most a few minutes, duration, it will be apparent that the interruption of the supply of current will normally cause a variation of only a fraction of a second from the correct time.

The induction. motor and the synchronous brake The coil 50, which is adapted to be connected to a suitable source of alternating current by conductors 52 and plug 53, is wound about the inwardly projecting ends of laminations 53, 55,

5B, 51, 58 and 59 (Figs. 7, 9, 16, 17 and 18),, which are secured to each other by bars 59 and to the frame plate 22 by bolts 52, 63. The laroinations 5S and 53 are substantially E- shaped, the ends of the two lower horizontal portions of these laminations being shaped to form field poles for a hard steel rotor 54 of the induction motor, a diametrically opposite pair of these poles being shaded by having a plurality of shortcircuited copper bars 55 pressed thereoyer. The rotor of the induction motor could be made with induction bars, or could be a disc of cold rolled steel, but a hardened steel disc is preferred because of the greater torque which it is capable of developing. The laminations of the unshaded poles are preferably secured against vibration by bolts or rivets 53. The inner laminations 5'I, 59, of which there are several pairs, have diametri- V cally opposite inwardly projecting portions 5?. r and 59 which form poles for the rotor III of the synchronous brake; These poles are toothed to register with the teeth formed upon the rotor 15, as shown in dotted lines in Fig. 7. A plurality of pairs of laminations 53, 55 are positioned between the iaminations 56,58 and 57, 59, respectively, forming spacers therefor.

The rotor I0 may be formed of two identical laminations secured to a hub I2, the latter being non-rotatably secured to a shaft 14. The rotor 84 of the induction motor is pressed over a pinion I6 which is freely rotatable upon the shaft I4. The shaft I4 is rotatably mounted in suitable bearings formed in plates I8, 80 secured to frame plate 24 and bearing plates 82, 84 secured to frame plate 22. These bearing plates are made of a phenolic condensation product or similar material, and will hereinafter be described in greater detail.

The year trains and spring motor As best shown in Figs. 9 and 10, the pinion I5 is in mesh with a gear 88, which is secured on a sleeve 8! and freely rotatable upon a shaft 88, and has a. pinion 90 secured thereto. The'pinion carrying a pinion H0. The pinion IIII meshes with a gear H2 formed on the spring drum N4, the latter being mounted for free rotation upon the spring shaft Iii. A spiral clock spring II8 has its outer end secured to the spring drum and its inner end secured to the shaft 6.

The above described gear train thus is adapted to transmit power from the induction rotor 54 to the spring drum to wind the same, or rather, in normal operation, to maintain the same'wound. A similar gear train is utilized for transmitting the power of the spring to the synchronous brake. This gear train comprises gear I20 secured to the shaft III; and meshing with pinion I22 secured to shaft I08. The pinion I22 is rigid with a gear I24, the latter meshing with the pinion I25, freely rotatable on the shaft I02. A gear I28 is fixed to the pinion I26 and meshes with a pinion rcured thereto, the latter meshing with a pinion I34 secured to the shaft 58. A gear I36, rigid with the pinion IB 'I, drives a pinion I38 secured to the shaft I4. As previously stated, the rotor III is rigidly secured to the shaft 14. The last described gear train is thus adapted to transmit the driving energy of the spring M8 to the rotor assembly of the synchronous brake. The rotor 55 of the induction motor and the rotor III of the synchronous brake rotate in the same direction, and it will be noted that corresponding gears of the two trains are in each instance mounted on the same axis, and since the gear ratios are identical, each gear which is rotatable on a shaft will, during normal operation of the clock, rotate in the same direction and at the same speed as the shaft upon which it is mounted. Thus there will be extremely little wear in the bearings of the gears and pinions which are rotatably mounted upon the shafts, the only bearings continuously subjected to wear being those of the rotatable shafts. By providing the gearing in this manner, I have in effect elimi nated one-half of the bearings which would otherwise be necessary. Due to the improved bearings which I have provided for the ends of the shafts, the wear upon bearings has been greatly reduced and the clock mechanism made more durable. It will be understood that the only time when the gears which are rotatably mounted upon a shaft rotate relative to the shaft is during intervals of current interruption when the train of gearing between the rotor 54 of the induction motor and the spring drum H5 is stationary, and following an interruption when the spring is rewound.

The gearing ratio is such that the shaft IIIB will rotate at one revolution per minute, and the second hand 44 may therefore be secured to the end 'of this shaft; The shaft III has a pinion I40 secured thereto which meshes with a gear I42 rotatably mounted upon a shaft I44. The gear I is rigidly connected to a pinion I45 which meshes with a gear I48 rotatably mounted upon the shaft I". The latter gear is rigidly connected to a sleeve I 50 surrounding the shaft I III! and at its end carrying the minute hand 42. The gear I48 is frictionally rotated with the shaft I08 by a spider spring I49 compressed between the pinion I40 and the side of the gear I48. The

pinion I52 secured to the gear I48 meshes with a gear I54 secured to the shaft I44. The gear I54 has a pinion I55 secured thereto and projecting outwardly through the frame 20, the pinion I56 meshing with a gear I58 secured to the hour hand sleeve I68. It will thus appear that The hands of the clock may be set in the usual manner by rotating a thumb nut I62 secured to a stem I64, the latter being rotatably mounted in the frame platesof the clock and having a. pinion I66 secured thereto and meshing with the pinion I54.

A knurled starting thumb piece I68 is secured to a shaft I18, the latter being mounted for rotation and axial movement in the frame plates 22 and 24 and carrying a pinion I12, adapted to mesh withgear I82 when the thumb piece I68 is pushed inwardly. A spring I14 normally holds the pinion I12 disengaged from the gear I32. This thumb piece is used only in starting the clock, as will hereinafter appear.

The drum 4 of the spring motor has a ratchet wheel I16 secured thereto or formed integrally therewith. A pawl I18, freely pivoted at I88 to I the outer end :of an arm I82, rests by gravity.

upon the drum I I4 and has a tooth I84 adapted to engage the teeth of the ratchet wheel I18. The arm I82 is rigidly secured to a sleeve I86 which is capable of only limited rocking movement, and thus prevents clockwise movement of the ratchet wheel I16 except through a small angle, as indicated in Fig. 6 by the full and dotted line positions of the pawl I18. A stop pin'I88 I limits counter-clockwise movement of the sleeve I86 by arresting the movement of the arm I82.. The centrifugal brake mechanism A hub I88 (Figs. and 9) is rotatably mounted on the shaft 14 and has secured thereto a bar pair of plates made of-a phenolic condensation product or similar material. In Fig.8, one of the inner bearing plates 88 is shown as having a same material as plate 88. The plates 18 and 88 are secured to the frame plate 24 by means of suitably spaced rivets 232. There is of course I a minute crevice between the two plates 18, 88,

.which permits gradual seepage of the oil from the perforations 238 to the bearings. In this manlubricant for a largenumber of years.

this type of bearing is extremely useful in con- N2, the outer ends of which have inwardly and sidewardly bent flanges I94. Leaf springs I96 are riveted to the flanges I94 and at their ends carry weights comprising two portions I98 and 288, secured together and to the ends of the springs I96 by screws-282. A head 284 is rigidly secured, to the end of the shaft 14 and has a diamet'rical slot 286 formed therein. A wire spring 288 is bowed to have its ends projecting through openings 2I8 formed in the bar I92 and its mid portion engaged in the slot 286. This spring has the double function of resiliently conmeeting the bar I92 for rotation with the shaft 14 and drawing the hub- B98 against the end of the head 284 so that a certain amount of friction will be present between the head and the hub I98. The centrifugal'weight's are partially enclosed in a circular race 2I2, which is substantially Z-shaped in cross section and is pivoted to the frame plate 24 by a bolt or rivet 2I4. The

race has an inwardly projecting lug 216 which extends through an opening 2I8 formed inthe frame plate 24. A pair of blocks 228 arethreaded to receive adjusting screws 222 and 228 to limit the extent of pivotal movement of the race 2I2. The race 2I2 is normally held in its' lowermost position with the ear 2I6 resting upon the" adjusting screw 224 by the force of. gravity, but is adapted to be raised upon an interruption of the supplyof; current by means of an arm 226, which is secured to the sleeve I86. It will be recalled that the sleeve I86 is rocked clockwise (Figs. 3 and 11) by the pawl l18jand arm I82 whenthe current is interrupted, and the spring drum permitted to rotate clockwise.

mounted for rotation in bearings composed of a lows:

Operation Assuming that the plug 54 has been connected to a-source of alternating current of regulated frequency, the operation of the clock is as folmade. the rotor 64 of the induction motor, due to the rotating field formed by the shaded poles of the laminations 56, 58, commences rotating, and through the gear train between. it and the spring drum H4 commences winding up the spring H8. The rotor 18 of the synchronous brake will be held stationary by the magnetic flux since its field is not rotating, but on the contrary its pole pieces have teeth which register 'withand attractthe teeth of therotor. The spring, even when fully wound up, is not sumciently strong to move the rotor 18 of the synchronous brake out of its magnetically flocked position. Thus, unless the synchronous brake is and rotate the thumb piece I68 clockwise. When the thumb piece is pushed in, the pinion I12 connected to its stem I18 engages the gear I32 so that when the thumb piece is manually twirled, the shaft 14 and all parts connected therewith are rotated, the rotor 18 of the synchronous brake being forcibly moved out of its magnetically locked position. As soon as the rotor rotates at any appreciable speed, the poles of the synchronous brake do not exert any great magnetic attraction until the rotor attains synchronousspeed. Manual rotation of the shaft '14 at much greater than synchronous speed is prevented by the frictional engagement of the weights of the centrifugal mechanism against the inside wall of the raceway 212. As the rotor 18 approaches synchronous speed, its magnetic field exerts a relatively powerful torque upon it,

, tending to prevent deviation from this synchronous speed. Unless some means are provided to.

dissipate energy at the instant that the rotor- 18 the rotor will not fall intostep. The theory and principles of the operation of the rotor with reference to its coming into synchronism are substantially the same as those of a similar rotorof a. synchronous motor, such, for example, asis shown and described in Patent ,No. 1,719,885,

' granted to me on July 2, 1929. In the present construction, the bar I 92', together with "the of clocks and' I As soon as a connection with the source isweights 200, forms the inertia member and corresponds to the inertia washer disclosed in said patent. It will be noted that the bar I92 is frictionally connected to rotate with the shaft because of the friction between its hub I90 and the head 204. The friction between these parts should be considerable, but must be small enough to permit of relative motion when the rotor falls into step. The spring 208 has sufiicient play and is sufficiently pliable that it does not materially interfere with the utility of the bar I52 and the parts carried thereby as an inertia means to insure falling into step of the rotor III of the synchronous brake, but of course causes the bar I92 and associated parts to rotate with the shaft 14 except for such minor relative rotation as is desirable to cause the rotor of the synchronous brake to fall in step and to prevent it from hunting.

Having brought the synchronous brake rotor 10 up to synchronous speed, it will continue to be driven by the spring H8 and will act as a nearly perfect governor to control the speed of unwinding of the spring in synchronism with the frequency of the alternating current supply. The rotor 64 constitutes a variable speed motor which is of the induction type. It is capable, however, of running at a speed several times the synchronous speed of the rotor I0, so that even though the rotor I is started substantially at the same time that the clock is connected to a source of alternating current, it will within a short time completely wind the spring H8, or at least will wind the spring to an extent where the torque from the spring tending to rotate the rotor 84 in a reverse direction is exactly equal to the torque developed by the rotor 64 when rotating at the same speed as the rotor 10. While the clock is operating in this manner, the pawl I" will be in the position shown in dotted lines in Fig. 6, since the ratchet wheel I16 will be rotating counterclockwise. Thus the raceway 2" will be in its lower position with its lug 2l8 resting against the lower adjusting screw 224. In this position the weights do not hit against the raceway when the shaft 14 is rotating at synchronous speed. The centrifugal mechanism thus has no effect upon the rotation of the shaft I4 except to act as an antihunting means.

Upon an interruption in the supply of the current to the clock, the rotor M will of course be incapable of exerting a torque, and the spring III will rotate it in the reverse direction. This reverse rotation will, however, be arrested within a very short time by the pawl I'll. which will be moved from the dotted line to the run line position (F156), and during this movement pivot the arm 226 and raise the raceway 2|2 until its lug 2N abuts against the upper adjusting screw 222. Thereafter, further reverse rotation of the induction rotor 64 is prevented. The rotor ll of the synchronous brake continues rotation at substantially synchronous speed. There is, of course, a slight tendency for all the parts connected to the shaft 14 to rotate at an increased speed. This tendency is counteracted in a large measure by the inertia of all the rotati g parts and by the frictional drag exerted as the induction rotor N rotates in the reverse direction. It has been found that during the interval that the pawl I18 moves froni dotted to full line position (Fig. 6), the speed of rotation of the rotor II will remain at so close to synchronous speed that it will seldom slip even a single tooth. (This test may be made by observing the rotor under the illumination of a neon glow lamp held adjacent the rotor of the synchronous crake and then disconnecting the supply of current to the clock.)

When the pawl I18 move to its full line position and the raceway 2i? raised with its lug 2| against the adjusting screw 222, the lower portion of the raceway will be inposition frictionally to engage the weights 200 should the speed of the shaft H exceed its normal synchronous speed. This centrifugal regulating mechanism has been found to be extremely accurate. During a period of half an hours run, the cumulative error is found to be not more than a few seconds. Since interruptions in the supply of current to an electric clock are usually of comparatively short duration, the centrifugal mechanism can ordinarily cause an error of only a fraction of a second for such period, usually of less than a minutes duration.

Upon resumption of current supply to the clock, the induction rotor will of course again commence rotation and again wind the spring Ill. As it winds this spring it will permit the pawl I18 to resume its normal position (shown in dotted lines in Fig. 6), whereupon the raceway 2l2 will again drop to its lower position with its lug 2" resting on the lower adjusting screw 224. As soon as the supply of current is resumed, the rotor III of the synchronous brake will immediately fall into step and again act as the effective brake to control the speed of operation of the clock. It will be noted that the raceway 2 forms a partially enclosed chamber for the weights 2llil, thus decreasing the air friction on these parts; Theory of operation In order that the clock may operate as above described, certain fairly definite quantitative relationships must be present. As previously stated.

rent is turned off (and hence no counter torque exerted by the braking rotor III). the spring Ill must be capable of developing sufllcient torque to overcome the friction in the sear train between the shaft I I6 and the shaft II, to overcome the friction in the auxiliary gear train driving the hands of the clock, and to overcome the friction exerted upon the shaft I4 and the centrifugal governing mechanism. The spring Ill must not, however, be capable of exerting suflicient torque to overcome the friction of the gear train between the shaft l i6 and the shaft I4 and at the same time to move the rotor-III out of its magnetically "lock "positio Instead of moving the raceway 2|2 from one I position to another when the current is turned off, the raceway could be adjusted and held firm- 1y fixed in a position where the weights 2" would just miss striking against the'raceway.

In such a construction, the synchronous brake would maintain the speed during the periodthat current is being supplied, and as soon as the current was interrupted, the shaft ll would slightly increase its speed of rotation until the 2,281,493 -weights contacted with the wall of the raceway. I

This would result in a temporarily slightly inthe weights 266, if the position of the raceway was not adjusted exactly correctly, occasionally to strike against the raceway, thus making the clock slightly noisy in operation. With the preferred construction previously described, this noise incidental to the striking of the weights 200 against the raceway occurs only during the periods of current interruption and thus serves auseful purpose in indicating that such interruption is taking place.

The pendulum speed governor In Figs. 12 and 13, I have illustrated a modified mechanical speed governing means which may, if desired, be substituted for the centrifugal mechanism previously described, although the latter has several advantages not present in the pendulum control mechanism. In the construction illustrated, the rotor 19' of the synchronous brake is rigidly secured to a shaft 14". A pinion 248 havingpa hub 242 is secured to the shaft 14- and meshes with a gear 246, which is rotat- -ably mounted upon a shaft 246. A crank disc 286 having a hub 252 is also rotatable upon the shaft 248 but is resiliently constrained to rotate with the gear 246 by a torsion spring 254, one end of which is secured to the gear 246 and the other end of which is anchored to the disc 286. The disc has a crank pin 256 which is connected by a link 258 with a pin 266 at the end of' an arm 262 formed integrally with a friction plate 264. The plate 284 is secured to the rod 266 of the pendulum by a bolt 216, the plate being pressed against a disc 212 of friction-material by a spider-shaped spring 214. The d ree of pressure exerted by the spring 214 may be readily adjusted by means of thethumb nut 218 threaded on the bolt 216. The pendulum rod is supportedby flat spring 280 suspended from any suitable support 282, eing secured to the support by a bolt 284. The lower end of the spring 286 is secured to the pendulum rod by ascrew 288. The pendulum has the usual bob 288, the "position of which may be adjusted by means of nut 29!! and. lock nut 292. A collar a pair of washers 29! which are mounted for free rotation upon the collar 289. These washers serve as a frictionally connected inertia means for aiding in causing the synchronous brake to fall into step and for minimizing hunting, as

z 289 is rigidly secured to the shaft 14 andcarries mal operation, the'shaft 14 will, through pinion 240, gear 246, crank disc 256, and link 258, oscillate the pendulum. It will normally be attempted to adjust the length of the pendulum, so that it will swing in exact synchronism with the alternating current supply. Such adjustment is, however, impossible due mainly to the slight variations in the frequency of the supply, and the pendulum is therefore adjusted so that it will tend to oscillate at a frequency slightly less than the frequency at which it is actually oscillated by the crank rod 258 when the synchronous brake is operating to retard the speed of rotation of the shaft 14 The degree of friction between the discs 264 and 212 is sufiiciently great that there will be, no relative movement between the plate 264 and the pendulum rod 266 during such normal operation. The pendulum is, however, continuously "crowded by its driving means.

When an interruption occurs in the supply of current, the speed of rotation of the shaft 14 will be accurately controlled by the pendulum. When the braking effect of the synchronous rotor brake 1|] is removed upon a current interruption, the full forceof the main driving spring will be eflective'to oscillate the pendulum and would,

unless deterrent means were provided, tend to increase the amplitude of oscillation of the pendulum'far beyond that permitted by the throw ofthe crank pin 256. The frictional connection between the plate 264 and disc 212 is therefore provided so that, as the pendulum tends to increase the amplitude of its oscillation beyond that permitted by the crank pin 256 and connecting link 258, there may be relative movement between the plate 264 and the disc. This relative movement between'these parts will result in dissipation of the excess energy provided by the main driving spring and thus permit the pendulum to oscillate only at itsnormal amplitude and to maintain its time-keeping characteristics. If the frictional connection were not provided the parts of the pendulum driving mechanism would be subjected to excessive stresses and the period of oscillation of the pendulum would be materially shortened.

The spring 254 forms a resilient driving connection which tends to take up minor irregularities in the relative speeds of the pendulum and its driving gear 246,'and acts as a means to insure continuous harmonious oscillation of the pendulum even though the gear 246 is not rotating in exact synchronism with the. pendulum.

Balance wheel escapement mechanism As a second'altemative construction, I may utilize a balance wheel escapement mechanism to control the speed of rotation of the rotor shaft during intervals of current interruption.

In Figs. 14 and 15, I have illustrated one form of. a suitable mechanism of this type.

In this construction the rotor 10" of the synv chronous brake is rigidly secured to a shaft 14 to which is also'secured a pinion 294, the pinion meshing with a gear 298 secured to a shaft 298.

Inertia washers 299 are mounted-upon the shaft- 14 in the same manner as the inertia washers 2", previously described. A pinion 800 is freely rotatable upon the shaft 298 but is constrained to rotate with theshaft by a torsion spring 362, one end of which is secured to the gear 296 and the other end of which is stoked to the pinion control the speed of the clock. During such nor- .7. 904

868. The pinion 300 is in mesh with a gear which is rigidly secured to an escapement wheel 308 suitably mounted on a shaft 308. The pallets of anchor 3H1, secured to a pivotally mounted shaft 3 l 2, are engageable with the teeth of the escapement wheel 306 and are operable to oscillate a balance wheel 3. The balance wheel is preferably mounted in the usual manner, having a hair spring 3H5, one end of which is anchored at tilt! and the other end of which is secured to the balance wheel staff 320. Suitable hair spring tension adjusting means (not shown) may of course be provided.

In order to be operative forv the desired purpose in combination with the previously described clock, the balance wheel escapement mechanism must have the property of increasing its speed of oscillation with increased driving power. This may be accomplished in various ways, the one illustrated being the provision of a stop pin 322 on the balance wheel which is adapted to strike against a fixed stop 32 at both ends of its travel. Thus, if the balance wheel tends to oscillate at a frequency less than that required to permit rotation of the shaft 14 at its synchronous speed, the spring 302 will have its tension increased and a greater force exerted upon the escapement pallets, and thus tend to oscillate the balance wheel through an ever increasing are. When thus endeavoring to oscillate through an angle approaching 360, the pin 322 will at both ends of its stroke strike against the fixed stop 324 and the balance wheel will thus complete its oscillatory cycle in a shorter time.

In normal operation of the clock with the current on, the rotor of the synchronous brake will of course govern the speed of operation of the clock, and during such normal operation the balance wheel escapement mechanism will merely act idly. When, however, the supply of current to the synchronous brake is interrupted, the balance wheel escapement mechanism will become effectiveto controlthe speed of rotation of the shaft 14 This balance wheel escapement mechanism does not have all the advantages which are present in the preferred means to control the speed of operation of the motor; said means comprising an electric synchronous brake supplied with alternating current of regulated frequency, a member rotated by said motor, an element resiliently secured to said member and movable outwardly from the axis of rotation thereof, a stop normally stationary with respect to said member, and means for positioning said stop in the path of outward movement of said element thereby to impede rotation of said member at greater than a predetermined speed. said last named means being energized upon an interruption in the supply of current to said synchronous brake to move to operative position.

2. In a time-keeping device, the combination of an, induction motor, asynchronous brake, a spring, a frame supporting said motor, brake and spring, and a pair of gear trains one connecting said brake and spring and the other connecting said motor and said spring, said gear trains comprising a plurality of shafts rotatably mounted in said frame, each shaft having a gear and pinion fixed thereto and a gear and pinion rotatable thereon, the fixed and the rotatable gears and pinions normally rotating in the same direction.

3. A clock mechanism having a frame, a spring motor, and a pair of independent gear trains, said gear trains comprising a plurality of rigidly joined gear and pinion assemblies, a plurality of shafts rotatably mounted in said frame, each of said shafts, carrying a pair of gear and pinion assemblies, one of the assemblies being rigidly secured to the shaft and the other assembly being rotatable relative to the shaft, and both of said pairs of assemblies normally rotating in the same direction at approximately the same speed, one of said pairs of gear trains being connected to said spring motor to supply energy thereto and the other to withdraw energy therefrom.

4. In a device having a timing function, the combination of mechanism for utilizing the timing function, means to drive said mechanism, an alternating current source, brake means responsive to the alternations of the current from said source for limiting the speed of operation of said mechanism, centrifugal speed governing means connected to said mechanism, and means and a frictional yieldable driving connection between said motor and said pendulum.

6. In a time-keeping device, the combination of a shaft, a synchronous electric brake rigidly secured to said shaft, a crank, a yleldable resillent driving connection betweensaid shaft and said crank, an oscillatable pendulum, and a frictional driving connection between said crank and said pendulum.

'7. In a time-keeping device, the combination of an energy storing motor, a synchronous electric brake connected to a source of alternating current, driving gearing connecting said motor with said brake, an induction motor, driving gearing connecting said induction motor and said energy storing motor whereby energy may be transferred from the former'to the latter, a pendulum, and means for driving said pendulum from energy derived from said energy storing motor, said means including a yieldable spring and a frictional driving connection.

8. In a time-keeping device, the combination of an energy storing motor, a synchronous electric brake, means for connecting said synchronous electric brake to a source of alternating current, an induction motor for supplying energy to said energy storing motor, means for preventing said energy storing motor from driving said induction motor in a reverse direction upon interruption of current to the latter, a mechanical speed govzeroing mechanism driven by said energy storing motor in synchronism with said brake, and control means for regulating said mechanism upon operation of said second-named means.

9. In combination, a spring motor, a variable speed electric motor, a mechanism to be driven, a gear train connecting said spring motor and said mechanism, and a second gear train connecting said electric motor and said spring motor, one of said gear trains having a gear secured to a rotatable shaft and the other oi'said trains having agear mounted for rotation on said shaft, said gears-being arranged normally to rotate in the same direction at substantially the same speed.

-10. In combination, a spring motor, a variable speed electric motor, amechanism to be driven, a gear train connecting said spring motor and said mechanism. and a second Bear train con-U functioning automatically under certain abnormal conditions of operation of said balance wheel to increase the frequency of said balance wheel whenever'the amplitude thereof is increased to a predetermined degree.

12. In a clock, the combination of an escapement mechanism comprising a balance wheel, said wheel having a projection thereon, a synchronous electric motor, means actuated by said motor for controlling the oscillations of said balance wheel, and resilient means adapted to be engaged by said projection on the balance wheel when the amplitude of motion of said wheel is maintained beyond a predetermined degree .by said oscillation controlling means.

13. In a time keeping device, the combination j of a motor, a synchronous electric brake and an adjustable mechanical'speed governor both connected to be driven continuously by said motor, the normal adjustment of said governor permitting rotation of said brake at greater than its synchronous speed, and means actuated from said motor and operable upon an interruption oi the current supply to said brake to' change the adiustment 01 said governor, whereby said governor will become eflective to prevent the speed of said brake from exceeding the normal synlchronous speed of the latter.

LAURENS HAMMOND. 

